diff --git a/src/mod_ffi.c b/src/mod_ffi.c
index 401f9995..f9fbcff3 100644
--- a/src/mod_ffi.c
+++ b/src/mod_ffi.c
@@ -844,8 +844,8 @@ static JSValue js_get_cstring(JSContext *ctx, JSValue this_val, int argc, JSValu
 }
 
 
-static JSValue TJS_NewUint8ArrayShared(JSContext *ctx, uint8_t *data, size_t size) {
-    return JS_NewUint8Array(ctx, data, size, NULL, NULL, true);
+static JSValue TJS_NewUint8ArrayExternal(JSContext *ctx, uint8_t *data, size_t size) {
+    return JS_NewUint8Array(ctx, data, size, NULL, NULL, false);
 }
 
 static JSValue js_ptr_to_buffer(JSContext *ctx, JSValue this_val, int argc, JSValue *argv) {
@@ -855,7 +855,7 @@ static JSValue js_ptr_to_buffer(JSContext *ctx, JSValue this_val, int argc, JSVa
     JS_TO_UINTPTR_T(ctx, &ptr, argv[0]);
     size_t sz;
     JS_TO_SIZE_T(ctx, &sz, argv[1]);
-    return TJS_NewUint8ArrayShared(ctx, ptr, sz);
+    return TJS_NewUint8ArrayExternal(ctx, ptr, sz);
 }
 
 static JSValue js_deref_ptr(JSContext *ctx, JSValue this_val, int argc, JSValue *argv) {
@@ -916,7 +916,7 @@ void js_ffi_closure_invoke(ffi_cif *cif, void *ret, void **args, void *userptr)
     JSValue *jsargs = js_malloc(ctx, sizeof(JSValue) * cif->nargs);
 
     for (unsigned i = 0; i < cif->nargs; i++) {
-        jsargs[i] = TJS_NewUint8ArrayShared(ctx, args[i], ffi_type_get_sz(cif->arg_types[i]));
+        jsargs[i] = TJS_NewUint8ArrayExternal(ctx, args[i], ffi_type_get_sz(cif->arg_types[i]));
     }
     JSValue jsret = JS_Call(ctx, jscl->func, JS_UNDEFINED, cif->nargs, jsargs);
     for (unsigned i = 0; i < cif->nargs; i++) {
diff --git a/src/vm.c b/src/vm.c
index 277a108a..b47278e8 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -97,9 +97,7 @@ static const JSMallocFunctions tjs_mf = {
 
 /* SharedArrayBuffer functions */
 
-#define TJS__SAB_MAGIC 0xCAFECAFECAFECAFEULL
 typedef struct {
-    uint64_t magic;
     int ref_count;
     uint8_t buf[0];
 } TJSSABHeader;
@@ -112,15 +110,12 @@ static void *tjs__sab_alloc(void *opaque, size_t size) {
     TJSSABHeader *sab = tjs__malloc(sizeof(*sab) + size);
     if (!sab)
         return NULL;
-    sab->magic = TJS__SAB_MAGIC;
     sab->ref_count = 1;
     return sab->buf;
 }
 
 void tjs__sab_free(void *opaque, void *ptr) {
     TJSSABHeader *sab = (TJSSABHeader *) ((uint8_t *) ptr - sizeof(TJSSABHeader));
-    if (sab->magic != TJS__SAB_MAGIC)
-        return;
     int ref_count = atomic_add_int(&sab->ref_count, -1);
     assert(ref_count >= 0);
     if (ref_count == 0)
@@ -129,8 +124,6 @@ void tjs__sab_free(void *opaque, void *ptr) {
 
 void tjs__sab_dup(void *opaque, void *ptr) {
     TJSSABHeader *sab = (TJSSABHeader *) ((uint8_t *) ptr - sizeof(TJSSABHeader));
-    if (sab->magic != TJS__SAB_MAGIC)
-        return;
     atomic_add_int(&sab->ref_count, 1);
 }